Cast dental prosthesis and method of making same



Sept. 8, 1970 A'. B.WEINSTEIN ETAL 3,527,861

CAST DENTAL PROSTHESIS AND METHOD OF MAKING SAME Filed Feb. 6, 1967 FIG.2

INVENTORQ ABRAHAM B. WEINSTEIN BY JACOB B|sco w ATTORNEY United StatesPatent 01 fice 3,527,861 Patented Sept. 8, 1970 3,527,861 CAST DENTALPROSTHESIS AND METHOD OF MAKING SAME Abraham B. Weinstein, 23 RalseyRoad S., Stamford,

Conn. 06902, and Jacob Biscow, 70 E. 8th St., Brooklyn, N.Y. 11215 FiledFeb. 6, 1967, Ser. No. 614,334

Int. Cl. A61c 13/04, 13/08 US. Cl. 264221 13 Claims ABSTRACT OF THEDISCLOSURE The method of casting flowable materials in a vacuum by firstconnecting an air tight mold to a container filled above the connectionwith the casting material, exhausting air therefrom, and thereafterslowly lowering the vacuum and thereby forcing the flowable materialinto the air tight exhausted mold until filled with the castingmaterial.

This invention relates to cast parts and to a method of casting suchparts.

In dentistry, cast parts may consist of inlays, bridges, crowns, andother prosthetic appliances. Hitherto they were made by the lost waxprocess, sometimes employing centrifugal casting or other techniques foreliminating voids in the castings.

An object of the present invention is to provide a cast part which ismore precisely molded, free-r of voids, and more dense than parts madeby previously used processes in the dental arts.

We accomplish these and other objects and obtain our new results as willbe apparent from the casting and the method of making the same describedin the following specification, particularly pointed out in the claims,and illustrated in the accompanying drawing, in which FIG. 1 is a waxreplica of a part it is desired to cast, and

FIG. 2 is a cross-sectional view partly in side elevation of a vacuumforming and containing apparatus for casting the part.

FIG. 3 is an enlarged cross-section of the mold.

Broadly the invention comprises the formation of the cast part in avacuum. In a specific application of our process, We may first make ofwax or its equivalent, a replica or pattern of the part to be cast, asis commonly done in the dental art, and in some industrial applications.Such a replica is shown in FIG. 1. This is preliminary to manufacturinga mold of the replica.

If the pattern can be destroyed in the process of making the mold, thereplica may then be covered with a thin surface adhering material 12which can be electroplated. One such material is a fine silver powdercontaining liquid known as Barnett Silverizer, made by Precious MetalsResearch Works of Brooklyn, NY. Any other suitable thin adherent,conducting coating for electroplating nonconductors, as is known in theprior art, will do.

The pattern is then provided with a transparent tube 16 open at one endonly, and attached at the open end to the wax pattern, a sprue section18 built up at the other end of the pattern, and the pattern and spruecopper plated as at 14, to the desired thickness, say .010 inch. At thispoint the wax replica 10 is heated and the wax withdrawn from the copperplated mold through the sprue opening. The mold is then attached to theneck 24 of a receptacle 26. The entire mold and all joints are finallysealed with a compound 22, allowing the transparent tube 16 to re mainvisible. The sealing compound used may be made of wax.

The receptacle 26 has an opening to allow the material 28 supplied forcasting to enter the neck 24 into the mold. If the receptacle is alsoused as a mixing vessel, a paddle 30 for mixing the material to be cast,and conforming to the vessels inner surface 29 may be employed.

The mixing material may be a porcelain based mix and its hardener, suchas is disclosed in copending application entitled Cast Porcelain DentalProsthesis and Method of Making the Same, Ser. No. 335,305, filed Jan.2, 1964, now US. Pat. No. 3,400,097.

This material is capable of flowing into the mold and is hardenable whencast.

The casting operation is performed within an evacuated apparatus orshell 32. It is preferably made of glass or transparent plastic topermit the molded material in the transparent tube 16 to be observed. Inorder to simplify the construction, only a single outlet to the vacuumchamber is provided through the base 34 upon which the glass shell isseated and sealed. A conduit 36 connects the base to the vacuum pump 38.A release valve 40 is positioned on the conduit 36, connecting to theatmosphere for terminating the vacuum in the chamber. Within the shell astand 42 is supported on the base 34. Upon the stand, the vessel 26 isplaced, to which the mold is affixed. The paddle 30 is operated by amotor 44, also secured to the stand by means of bracket 46.

To reduce the number of connections to the vacuum chamber, aself-contained unit for driving the motor is provided. It comprises asource of energy, namely the battery 48, secured to the stand by arm 50,a flexible diaphragm pressure-controlled switch 52, mounted to thebattery by support '61, and a fixed contact 54, all connected andsupported in a manner hereinafter described.

The flexible diaphragm 56 of switch 52 carrying a movable contact 58 ismounted to a sealed air containing chamber 60. When a vacuum is formedinside the glass shell, the flexible diaphragm is outwardly expandeduntil movable contact 58 engages fixed contact 54 mounted to the stand.The current from the battery is then allowed to pass through connections62 and 64 respectively by reason of the closed circuit through contacts58 and 54, into the motor 44, which then proceeds to rotate the paddle30 mixing the materials in the mixing receptacle.

When the vacuum pressure is slowly reduced at valve 40, the flexiblediaphragm 56 is thereby allowed to retract towards the sealed chamber60, pulling the movable contact 58, away from stationary contact 54,opening the circuit and stopping the motor.

The method of casting is as follows: the mixing receptacle and attachedmold are placed in position on the stand, and the vessel filled with asmall excess of material to be cast into the desired form. The valve 40is then closed, the transparent shell suitably sealed to the base, andthe vacuum pump started.

At the moment the shell is satisfactorily exhausted, the movable contact58 is designed to engage contact 54, closing the electrical circuitinside the shell thus starting the motor. The thorough mixing of thecasting material is thus initiated and continues until the vacuum isbroken. This is accomplished by slowly opening valve 40 and stopping thevacuum pump. The flexible diaphragm of -the switch becomes lessdistended until the contacts separate and the circuit opened, stoppingthe motor and the mixing operation. The casting material is slowlyforced into the mold by the incoming air in the chamber, until thematerial is visible in the transparent tube 16 signalling the completionof the filling operation. When further movement of the material in thetransparent tube ceases, the valve is fully opened, the shell removed,and the mold removed from the receptacle.

When the porcelain based casting has become hardened by elapsed time orcured by heating, or whichever process is employed for hardening thecasting material, the mold is broken or separated from the casting, thesprue and tube 16 removed, the casting 66 trimmed, providing anextremely accurate replica of the desired part.

We have found that air should be allowed to enter the exhausted chamberslowly to properly fill the mold, and that the time is dependent on theviscosity of the casting material. Using the compound described in thecopending application, the filling operation for the average inlayshould take about 30 seconds. A large restoration may take as long asminutes.

It may be noted that the mold may be made of metal, or other materialsthat may be readily separated from the cast part, and in two or moresections which are separated to release the casting. It is of courseimportant that the mold be sealed at all joints to permit the castingmaterial only to enter the mold through the sprue opening when thevacuum is broken.

The result is an extremely dense cast part, free of voids in the surfaceof the part and in the cast material itself.

We have thus described our invention, but we desire it understood thatit is not confined to the particular form or uses shown and described,the same being illustrative, and that the invention may be carried outin other ways without departing from the spirit of our invention, andtherefore we claim broadly the right to employ all equivalentinstrumentalities coming within the scope of the appended claims, and bymeans of which, objects of our invention are obtained, and new resultsaccomplished, since the particular embodiment herein shown and describedis only one of the many that can be employed to obtain these objects andaccomplish these results.

We claim:

1. The method of casting material in a mold from a vessel containing thecasting material, which method comprises the steps of connecting themold through a sprue to the vessel, evacuating the air from the vessel,casting material, and the mold cavity through the casting materialwithout substantially filling the mold cavity; and thereafter openingthe vacuum to pressure fill the mold cavity completely with the castingmaterial.

2. The method of claim 1 in which the vessel, the casting material andthe mold are positioned in one chamber during evacuation.

3. The method of claim 1 in which the casting material in the vessel ismixed while the vessel is evacuated.

4. The method of claim 3 in which the mixing in the vessel is begun whenthe vacuum reaches a predetermined degree in the chamber.

5. The method of claim 1 in which the casting material is sueked intothe mold from the vessel through a passageway extending outside themold.

6. The method of claim 4 in which the mixing operation is automaticallystopped when the vacuum is opened to the atmosphere.

7. The method of claim 5 in which the mold is provided with a tubularextension having a closed end positioned oppositely of the passageway,having a size sufiicient to permit the casting material to enter.

8. The method of claim 7 in which the tubular extension is madetransparent to permit the contents to be visible.

9. The casting formed by the process of claim 1.

10. In the method of claim 1 of preparing a cast part from a mold, thestep of preparing a wax pattern in the exact shape it is desired toreproduce, applying a sprue to the wax pattern, coating the pattern witha layer of conducting material, electrolytically depositing a layer ofmetal over the coating to form a rigid shell, and thereafter heating themold and pouring the wax from the mold.

11. The method of claim 10, in which a reinforcing and sealing materialcovers and seals the mold.

12. The method of claim 10 in which a transparent tube is attached tothe wax pattern.

13. The method of claim 10 in which the mold is connected to a castingmaterial dispensing receptacle, and sealed thereto, about the moldopening.

References Cited UNITED STATES PATENTS 1,644,543 10/ 1927 Richmond 264-1,991,009 2/1935 Browne et al. 264-101 2,317,008 4/1943 Werner 264-162,477,273 7/1949 Tognola 264-102 2,566,596 9/ 1 Cantor 264--1022,803,054 8/1957 Kohring 264-101 3,059,278 10/1962 Daniel 2641023,271,491 9/1966 Mikkelborg 264-102 2,490,193 12/ 1949 Barr. 2,696,02212/ 1954 Steinbock et al. 2,877,494 3/ 1959 Wright et al. 3,005,232 10/1961 Steinbock et al. 3,064,309 11/ 1962 Steinbock et al. 3,081,492 3/1963 Grzegorczyk.

" DONALD J. ARNOLD, Primary Examiner A. H. KOECKERT, Assistant ExaminerUS. Cl. X.R.

